1. Field of the Invention
The invention relates to a carbonization plant designed and built according to the Non-Recovery Process or Heat Recovery Process for the production of coke from coal.
2. Description of the Related Art
In the past years, a great deal of improvements had therefore been proposed to homogenize the feed of primary and secondary air in the upper and lower oven in order to ensure a planar heating of the coal/coke charge from top to bottom. It is thereby possible to shorten the operating time required for a complete carbonization of the coal charge and to increase economic efficiency. Nevertheless, present solutions just represent an approximation to a planar heating because primary air in the upper oven and secondary air in the lower oven can always be supplied only spot-wise via the oven ground area.
A high throughput rate is particularly important to achieve economic efficiency of a carbonization plant according to the Non-Recovery Process or Heat Recovery Process, hereinafter briefly referred to as NR/HR. It is primarily due to the fact that a prolonged operating time, i.e. less economic efficiency, is always to be assumed for this technology since compared with the conventional horizontal chamber technology the release of combustion gas can only be slightly influenced. The velocity of this carbonization technology can only be influenced by an even supply of air to the process at several stages to optimize combustion.
In the past years, a great deal of improvements had therefore been proposed to homogenize the feed of primary and secondary air in the upper and lower oven in order to ensure a planar heating of the coal/coke charge from top to bottom. It is thereby possible to shorten the operating time required for a complete carbonization of the coal charge and to increase economic efficiency. Nevertheless, present solutions just represent an approximation to a planar heating because primary air in the upper oven and secondary air in the lower oven can always be supplied only spot-wise via the oven ground area.
An example for the refractory build-up in the lower oven is presented in the top view shown in FIG. 1. The crude gas/waste gas mixture formed in the combustion chamber of the upper oven is supplied to the sole flues in the lower oven in 2 to 20 downcomer channels per oven. There it is completely burnt by addition of combustion air. The heat generated there serves for carbonization of the coal charge from the bottom, thus ensuring a shortened operating time and a high performance rate of the oven. To this effect, so-called secondary air is sucked through openings at the front side in the lower oven and rendered available via a ramified vertical channel system to the actual sole channel heating flues for secondary combustion of combustible gases. During this process, a multitude of short individual flames is created in the sole channels. The heat generated in these sole channel heating flues is then vertically supplied via heat conduction through the oven sole of the coal charge for carbonization of this coal charge. The illustration clearly shows that the multiple-channel setup of the lower oven hardly offers any possibility for increasing the number of secondary air stages and thus for raising the efficiency of secondary combustion. Such a solution would also entail an unreasonably high extra expenditure on calibration procedures in terms of process technology.
Moreover, in the sense of an environmentally friendly oven operation, it is required to reduce nitric oxide (NOx) emissions from an industrial plant to the greatest possible extent. Nitric oxides occur in processes of combustion of fossil fuels, e.g. coal, in the flame and in the surrounding high-temperature zone by a partial oxidation of the molecular nitrogen of combustion air as well as of the nitrogen bound chemically in the fuel. Thermally formed NO as the main NOx constituent develops from molecular nitrogen N2 in the flame by oxidation with molecular oxygen at temperatures>1300° C. Since temperatures of up to approx. 1450° C. may occur in a NR/HR oven, technical efforts are to be taken to reduce this thermal NO formation and thus the resultant ecological burden. The most significant theoretical possibilities for NO reduction are comprehensively outlined in the following illustration:                low air figure in total        arrangement of air stages        NH3 injection        steam/water injection        waste gas recirculation.        